First, the principle and structure of the type of pressure reducing valve is a valve automatically reduce the working pressure of the special device, which can reduce the high pressure of the valve before the pipeline to the required level after the valve. Pressure relief valve is widely used in high-rise buildings, urban water supply pipe network pressure over the area, mines and other occasions to ensure that the water supply system water points to obtain appropriate service pressure and flow. Because the water loss rate and waste degree are almost proportional to the water pressure of the water supply system, the pressure reducing valve has the effect of improving system operation and potential water saving. According to the statistics, the water saving effect is about 30%. Many types of pressure relief valve structure, the previous common thin-film, such as the spring-piston. The basic principle of the valve is to reduce the water pressure by the local resistance of the flow channel in the valve. The range of the water pressure drop is automatically adjusted by the pressure difference between the inlet and outlet of the film or piston connected with the valve flap. In recent years there have been some new type of pressure reducing valve, such as constant proportional pressure reducing valve. Constant pressure than the principle of decompression is the use of valve body floating piston hydraulic ratio control, import and export side decompression ratio and the import and export of piston area ratio is inversely proportional. This valve works smoothly without vibration; there is no spring in the valve body, so there is no spring rust, metal fatigue failure considerations; good sealing performance without leakage, so both under pressure (water flow) and then the static pressure 0 o'clock); Especially in the decompression does not affect the water flow. Pressure reducing valves are usually DN15 ~ DN400 and other specifications, the working pressure before and after the valve were <1MPa and 0.1 ~ 0.5MPa, pressure range of ± 5% to 10% error. It should be noted that although water flow through the pressure relief valve has a large head loss, it is generally energy efficient due to reduced water wastage and reasonable system flow distribution and improved system layout and operating conditions. Second, the basic performance of the valve (1) pressure regulating range: It refers to the output pressure of the pressure reducing valve P2 adjustable range, within the scope of this requirement to achieve the required accuracy. Regulating the pressure range and the main spring stiffness. (2) Pressure characteristics: It refers to the flow rate g is set value, due to input pressure fluctuations caused by the output pressure fluctuations. The smaller the output pressure fluctuation, the better the characteristics of the pressure reducing valve. The output pressure must be lower than the input pressure - the setting will not substantially change with the input pressure. (3) flow characteristics: It refers to the input pressure - timing, the output pressure with the output flow g changes in the holding capacity. When the flow rate g changes, the output pressure changes as small as possible. The lower the general output pressure, the smaller it fluctuates as the output flow changes. Third, the selection of pressure reducing valve selected according to the requirements of the type of pressure reducing valve and pressure regulator accuracy, and then select the maximum output flow according to the required diameter. When determining the air pressure of the valve, it should be greater than the maximum output pressure 0.1MPa. Pressure reducing valve is generally installed in the water after the scrubber, mist eliminator or setter before, and be careful not to import, export reverse; valve knob should be relaxed when not in use, in order to avoid the diaphragm often affected by compression deformation Its performance.